I have a can of Ovaltine crystals that has been in my cupboard for around 10 years now. Today I was going to throw it out, but thought I’d open it first. The can felt a bit heavy, like it was half full. But when I opened it, it appeared to be empty. Then I looked down to the bottom of the can, and saw a shiny disk of what appeared to be a smooth black liquid. But it was hard, and did not flow freely.

Apparently, Ovaltine crystals are actually a liquid, just an extremely viscous one. It reminds me of the University of Queensland Pitch Drop Experiment.